System and method for managing software upgrades in a distributed computing system

ABSTRACT

A system and method for managing software upgrades in a distributed computing system. The distributed computing system may include a plurality of nodes which provide one or more fault-tolerant services. The system and method perform software upgrades in a sequential or “rolling” manner (e.g., node by node). The rolling upgrade process allows all services and data of the distributed computing system to remain operable and available throughout the upgrade process.

TECHNICAL FIELD

The present invention relates generally to distributed computingsystems, and more particularly to a system and method for managingsoftware upgrades and downgrades in a highly scalable, distributedcomputing system. The present invention performs sequential or “rolling”software upgrades in a distributed computing system in a manner thatallows the entire system to remain operable and available during theupgrade process.

BACKGROUND OF THE INVENTION

Distributed computing systems, such as distributed file systems,typically include several system severs or components that areinterconnected through a network. The various servers and components ofthe system run software that controls and manages the various operationsof the computing system. Periodically, new upgrades, releases, additionsor patches may be created for the software running on the system. Forthe system to operate properly, this new software must be loaded ontoall of the servers and components of the system.

In order to upgrade the currently running software in any priordistributed computing system, the system is temporarily shut down and/ormade unavailable. Once the system is stopped, the software upgrades,releases, additions and/or patches are loaded onto all systemcomponents, and the system is rebooted. This process undesirably causesthe distributed computing system to be inoperable or unavailable forsignificant periods of time during the upgrade process (i.e., until theupgrade is complete throughout the system), thereby depriving users ofthe system from accessing and operating the system until the upgrade iscomplete.

It is therefore desirable to provide a system and method for managingsoftware upgrades in a distributed computing system, which performssoftware upgrades in the distributed computing system, while allowingthe system to remain operable and accessible throughout the upgradeprocess. Accordingly, the present invention provides a system and methodfor managing software in a distributed computing system having aplurality of nodes, which performs software upgrades in a sequential or“rolling” manner (e.g., node by node), thereby allowing the distributedcomputing system to remain operable and available throughout the upgradeprocess.

SUMMARY OF THE INVENTION

One non-limiting advantage of the present invention is that it providesa system and method for managing software upgrades in a distributedcomputing system, which performs software upgrades in a sequential orrolling manner, such that the distributed computing system remainsaccessible throughout the upgrade process.

Another non-limiting advantage of the present invention is that itprovides a system and method for performing rolling software upgrades ina distributed file system having multiple components or resources.

Another non-limiting advantage of the present invention is that itperforms rolling upgrades on a distributed computing system byinstalling a software release on a boot server and then, one by one,rebooting the various components of the system with the new software.The system assigns a “protected” status to any fault-tolerant componentthat has a “mirror” or duplicate component that is temporarilyunavailable. The system will not reboot any protected components untiltheir fault-tolerant status is recovered.

Another non-limiting advantage of the present invention is that itprovides a rolling software upgrade model for a distributed computingsystem that also supports rolling downgrades releases, to back out of anupgrade which proves undesirable or unsatisfactory.

According to one aspect of the present invention, a system is disclosedfor managing a software upgrade in a distributed computing system havinga plurality of nodes that provide at least one fault-tolerant service.The system includes at least one server which is communicativelyconnected to the plurality of nodes and which is adapted to receive asoftware release, and to upgrade each of the plurality of nodes with thesoftware release in a sequential manner, whereby the at least onefault-tolerant service remains available while the software upgrade isin progress.

According to a second aspect of the invention, a method is provided formanaging a software upgrade in a distributed computing system having aplurality of nodes that provide at least one fault-tolerant service. Themethod includes the steps of: receiving a new software release; andupgrading each of the plurality of nodes with the new release in asequential manner, whereby the at least one fault-tolerant serviceremains available while the software upgrade is in progress.

According to a third aspect of the present invention, a method isprovided for managing a software upgrade in a distributed file systemhaving a plurality of nodes that provide a plurality of fault-tolerantservices. The method includes the steps of: receiving a new softwarerelease; determining whether the new software release is compatible witha current release running on the distributed file system; initiating arolling upgrade process if the new release is compatible; performing therolling upgrade process by sequentially loading and rebooting each ofthe plurality of nodes with the new software release; and ensuring thatthe plurality of fault-tolerant services remains available throughoutthe rolling upgrade process.

These and other features and advantages of the invention will becomeapparent by reference to the following specification and by reference tothe following drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary distributed computing systemincorporating one embodiment of a system and method for managingsoftware upgrades on the distributed computing system.

FIG. 2 is a block diagram illustrating the general operation of thesystem and method for performing software upgrades, according to oneembodiment of the invention.

FIG. 3 is an exemplary block diagram illustrating a method forinstalling software onto the SMS/boot servers of the present invention,according to one embodiment of the invention.

FIG. 4 is an exemplary block diagram illustrating a method forinitiating a rolling upgrade, according to one embodiment of the presentinvention.

FIG. 5 is a schematic diagram illustrating the comparison between acurrent software release listed in a configuration database (CDB) andcompatible releases listed in a new software release.

FIG. 6 is an exemplary block diagram illustrating a method forperforming rolling software upgrades, according to one embodiment of theinvention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will now be described in detail with reference tothe drawings, which are provided as illustrative examples of theinvention so as to enable those skilled in the art to practice theinvention. The present invention may be implemented using software,hardware, and/or firmware or any combination thereof, as would beapparent to those of ordinary skill in the art. The preferred embodimentof the present invention will be described herein with reference to anexemplary implementation of a fault-tolerant distributed file storagesystem. However, the present invention is not limited to this exemplaryimplementation, but can be practiced in any distributed computing systemthat includes multiple hosts, resources or components that run softwarethat may be upgraded periodically.

I. General System Architecture

Referring now to FIG. 1, there is shown an exemplary highly scalable,distributed computing system 100 incorporating a system and method formanaging software upgrades, according to one embodiment of theinvention. The distributed computing system 100 has a plurality ofresources, including service nodes 130 a-130 n and a Systems ManagementServer (SMS)/boot server pair 116 a, 116 b. Each SMS/boot server 116 a,116 b may comprise a conventional server, computing system or acombination of such devices. Each SMS/boot server 116 a, 116 b includesa configuration database (CDB) 114 a, 114 b, which stores state andconfiguration information relating to the system 100. The CDB 114 a, 114b may include a “hosts” section that stores the attributes and status ofeach of the nodes of the system 100, including the identity of thesoftware release(s) that is operating on each of the nodes. One of theSMS server pair 116 a, 116 b (e.g., SMS/boot server 116 a) may serve asthe primary SMS/boot server, while the other (e.g., SMS/boot server 116b) may act as a backup, which is adapted to perform the same functionsas the primary SMS/boot server in the event that the primary SMS/bootserver is unavailable. The SMS/boot server pair 116 a, 116 b eachincludes hardware, software and/or firmware that is adapted to performsystem management services. Particularly, the SMS/boot server pair 116a, 116 b is responsible for management services such as starting,stopping, and rebooting service nodes, and for managing softwareupgrades on the various nodes of the system 100. SMS/boot server pair116 a, 116 b may also perform management services, such as the resourceprovisioning, configuration and allocation services described inco-pending U.S. Patent Application, entitled “System and Method forManaging a Distributed Computing System,” which is assigned to thepresent assignee and which is fully and completely incorporated hereinby reference.

It should be appreciated that in alternate embodiments the SMS/bootserver pair 116 a, 116 b may comprise a plurality of disparate devicesthat perform one or more of the foregoing functions. For example, thesystem may include separate dedicated boot servers and/or separatededicated SMS servers. In the following discussion, the SMS/boot serverpair 116 a, 116 b may be collectively referred to as the SMS/boot server116, and the CDB pair 114 a, 114 b may be collectively referred to asthe CDB 114. Furthermore, the term “n” is used herein to indicate anindefinite plurality, so that the number “n” when referred to onecomponent does not necessarily equal the number “n” of a differentcomponent. For example, the number of service nodes 130 a-130 n neednot, but may, equal the number of services 120 a-120 n.

Each service node 130 a-130 n within system 100 is connected by use ofan interface (e.g., 160 a 1-160 an, 160 b 1-160 bn, 160 n 1-160 nn) toat least a pair of switching fabrics 110 a-110 n, which may comprise forexample, but without limitation, switched Internet Protocol (IP) basednetworks, buses, wireless networks or other suitable interconnectmechanisms. Switching fabrics 110 a-110 n can provide connectivity toany number of service nodes, boot servers, and/or function-specificservers such as the SMS/boot server pair 116 a, 116 b.

In the preferred embodiment, each service node 130 a-130 n in system 100may include at least one service process 103 a-103 n, which can be, forexample but without limitation, a gateway process, metadata process, orstorage process for a file system. Each service node 130 a-130 nprovides a fault-tolerant service and preferably includes a primaryservice instance (e.g., service nodes 130 a 1-n 1) and one or morebackup service instances (e.g., service nodes 130 a 2-n 2). The primaryservice instance and its one or more backup service instances aresubstantially identical (e.g., have substantially identical components,functions and content), and in most cases reside on separate physicalmachine to ensure independent failure, thereby avoiding the primaryservice instance and its one or more backup service instances failingtogether. The primary and backup services may maintain fault-toleranceusing a suitable checkpointing technique, such as that described in U.S.patent application Ser. No. 09/997,877, entitled “Fault Tolerance UsingLogical Checkpointing in Computing Systems,” which is assigned to thepresent assignee and which is fully and completely incorporated hereinby reference.

Services 120 a-120 n typically provide different functions within adistributed computing system. For example, but without limitation, oneservice may provide a distributed, scalable, and fault-tolerant metadataservice (MDS), while another may provide a distributed, scalable gatewayservice (GS), a distributed scalable bit file storage service (BSS), orsome other service. Examples of metadata, gateway and storage servicesare described in U.S. patent application Ser. No. 09/709,187, entitled“Scalable Storage System,” which is assigned to the present assignee,and which is fully and completely incorporated herein by reference.

Each service node 130 a-130 n in system 100 may also include lifesupport service (LSS) processes 102 a-102 n. The LSS processes monitorthe state and operability of the components and services of thedistributed computing system 100 (e.g., whether each of the componentsis functioning properly). This state and operability information may becommunicated to the SMS/boot server 116, which may utilize theinformation in order to place a “protected” status on certain componentsor nodes during the upgrade process in order to ensure that all systemservices and information remain available throughout the upgradeprocess. The use of this protected status in the upgrade procedure ismore fully and completely discussed below in Section II.C. The SMS/bootserver 116 may also use the state and operability information todetermine how system resources should be allocated or modified toachieve certain user-selected performance attributes and functionality,as discussed in the above-referenced, co-pending U.S. PatentApplication, entitled “System and Method for Managing a DistributedComputing System.” The function of the LSS system is fully andcompletely described in co-pending United States Patent Application,entitled “System and Method for Monitoring the State and Operability ofComponents in Distributed Computing Systems,” which is assigned to thepresent assignee, and which is fully and completely incorporated hereinby reference.

Each service node 130 a-130 n in system 100 also includes an SMS agentprocess 101 a-101 n, which is a managed entity used by the SMS/bootserver 116 to remotely manage a service node (e.g., to start, stop, andreboot a service node). Each agent may include fault-tolerant softwareloading mechanisms that can be remotely directed by the SMS/boot server116 to load the necessary software onto the nodes. In one embodiment,the software for all nodes is stored in two separate boot serverportions of the SMS/boot server 116.

It should be noted that the components of the service nodes may receivemessages directly from the SMS/boot server 116 and from other componentsthrough the switching fabric 110 a-110 n, or alternatively, suchmessages may be mediated by another layer of communication software 104a-104 n, according to a known or suitable mediation scheme.

In accordance with the principles of the present invention, theforegoing nodes and services are provided for purposes of illustrationonly and are not limiting. The resources of the system 100 may be usedfor any function or service, for example but not limited to, a highlyscalable, fault-tolerant storage system. Furthermore, while only threeservices (i.e., services 120 a, 120 b, 120 n), and two SMS/boot servers(i.e., servers 116 a, 116 b) are shown, many more of each of theseservices and servers may be connected to one another via switchingfabrics, according to the present invention.

II. Operation of the System

Referring now to FIG. 2, there is shown a block diagram illustrating thegeneral operation of a system 200 for managing software upgrades in adistributed computing system, such as system 100 of FIG. 1. As shown inFIG. 2, a new software release 210 may be received by one of theSMS/boot servers 116, which will install the software on the remainingSMS/boot servers 116. The SMS/boot servers 116 will then determinewhether the installed software is compatible with software presentlyrunning on all of the nodes of the system (e.g., nodes 220-1 through220-N, which may represent nodes 130 a-130 n of system 100). If thesoftware is compatible, the SMS/boot servers 116 may perform a rollingupgrade of the software by sequentially loading the new software on eachnode in the system (e.g., on nodes 220-1 through 220-N), in a mannerwhich allows the system and all of its services to remain operable andavailable throughout the upgrade process. In one embodiment, aconventional user interface 230, such as a command line interface (CLI)or a graphical user interface (GUI), may be used to initiate or controlthe installation and/or rolling upgrade processes. The foregoingelements and steps, which are implemented in the management of theupgrade process, are described more fully and completely below.

A. Installing New Software Releases

FIG. 3 is a flow diagram 300, illustrating an exemplary method ofinstalling new software releases on SMS/boot servers 116, according toone embodiment of the present invention. In step 310, a new softwarerelease is received by the system 100. In the preferred embodiment, anew software release or “upgrade” may be received by system 100 in anyconventional manner, such as by loading the software onto one of theSMS/boot servers 116 by use of a conventional input device (e.g., a diskdrive) or by uploading the software from a remote system or network(e.g., by use of an ftp transfer or other suitable transfer protocol).

Once the software is received, the SMS/boot server 116 may check thesoftware to ensure that it is complete (e.g., that all necessarycomponents are present) and that no other noticeable errors exist, asshown in step 320.

The new release may then be installed onto all active SMS/boot servers116, as shown in step 330. In one embodiment, a software release maytake the form of a gzip-compressed tar archive file. The release may beinstalled by unpacking it with a “tar-zx” command (or the equivalentcpio command, if appropriate). The release will preferably include fullyqualified names, so that it installs in the correct place in a filetree. A system administration command to install software (e.g.,“install_software”) may be entered through an administrative interface(e.g., interface 230) to initiate or perform the installation. Theimplementation of the command will repeat the installation on allSMS/boot servers 116 (e.g., by copying the software from the firstmachine on which it is installed to the others). This may involvekeeping a temporary copy on first machine until it is installed on alllocations.

In the preferred embodiment, new software releases, which may includesoftware patches are labeled with a unique identifier (e.g., a 64-bitidentifier). A release may be installed in a distinct subtree on a bootserver (e.g., on SMS/boot server 116 a, 116 b), and may not beconsidered suitable for further use until it has been installed on allactive boot machines. For example, a new release may be stored under anassigned directory on a boot server, in a subtree corresponding to theunique identifier of the release. The subtree may include variousdirectories which constitute a constant part of the release, such asbinary and library directories. The release may contain all software,including kernel and other base system components, not just theproprietary software of the related distributed computing system.Architecture-specific components, such as executables, may be groupedunder their own directories.

Each subtree may contain a file (e.g., a release identifier file) thatidentifies the release (e.g., as a hexadecimal string), and, on anyexecuting machine, a file of the same name gives the current releaseidentifier for software executing on that machine. The identity of therelease(s) running on the nodes of system 100 may be maintained in areleases node or portion of the CDB 114.

After a copy of the new software is installed on each boot server, amanagement command records the presence of the new release by creating anode that identifies the release in the CDB 114, as shown in step 340.The node corresponding to the release that is presently being run by thesystem 100 may be assigned an attribute “_current”, which identifies therelease as the current release being run by the system 100.

Patch Releases

A new software release may also comprise a delta patch release. A deltapatch release may contain a file entitled “DeltaPatchRelease”. Wheninstalling a release, the SMS/boot server 116 will first look for theexistence of such a file. If present, the SMS/boot server 116 will firstextract the file and process it, before unpacking the release as usual.In the preferred embodiment, the file may contain lines in threeformats. First, a line of the form “BaseRelase nnn” specifies therelease on which the patch is based. If release “nnn” is not installed,the SMS/boot server 116 will refuse to install the patch. Otherwise, theSMS/boot server 116 will clone the base release directory tree as thetree for the patch release, and hard-link all files from the basedirectory tree into corresponding locations in the patch release tree.The SMS/boot server 116 will then search for lines of the form “Deletexxx”, and delete files “xxx” which may be included within the patchrelease tree, in order to remove unnecessary files. The SMS/boot server116 will then search for lines of the form “Rename xxx yyy” which may beincluded within the patch release tree, and rename files “xxx” to “yyy”within the patch release tree, in order to conform to the new release.The SMS/boot server 116 will then proceed to unpack the release asusual. Those of ordinary skill in the art will appreciate that thisprocess and patch configuration will enable rapid distribution ofrelatively small fixes via slow communication links, such as modems.

The patch may also include a “PostInstallation” script, which providesinstructions for the SMS/boot server 116 to perform after aninstallation is complete. The SMS/boot server 116 may search for this“PostInstallation” script at the top level of the installed software,and if it is present, run it to perform any post-installationoperations, such as reconstructing the boot images for the non-bootservers (to avoid having to include those images in patch releases).

Users (e.g., system administrators) may be allowed to selectivelyinstall a particular patch. Patches, however, are mutually exclusive atruntime. For example, since a given release specifies those releasesfrom which is an upgrade, one can only change from release A to patch A1and then patch A2 if A2 is an upgrade from A1, which is in turn anupgrade from A. In the preferred embodiment, the system will normallymaintain patches cumulatively, so that each new patch is a superset ofany previous patch on the same base. If branches arise, then one wouldnormally be unable to switch from one branch to another withoutdowngrading to a common ancestor or upgrading to a common descendant, aswill be appreciated by those skilled in the art.

B. Initiating Software Upgrades

FIG. 4 illustrates an exemplary method 400 for initiating softwareupgrades that may be performed by the SMS/boot server(s) 116, accordingto one embodiment of the present invention. In step 410, a softwareupgrade is requested. In the preferred embodiment, a systemadministration command (e.g., “upgrade_software”), with the identifierof the release to which the system is to be upgraded as an argument, maybe inputted through a conventional administrative interface (e.g., userinterface 230) to request a rolling upgrade.

In the preferred embodiment, upgrade requests and status informationregarding the upgrade requests are recorded and maintained in the CDB114. Entries may be created and viewed through an administrativeinterface (e.g., interface 230), and may be deleted by administrativerequest. In one embodiment, each entry may include the followingattributes:

FromRelease Hexadecimal release identifier to change from ToReleaseHexadecimal release identifier to change to CancelRequested (presentonly if cancellation is requested) Cancelled (present only if requesthas been cancelled) Started (present only if processing request hasstarted) Completed (present only if processing request has completed)Failed (present only if processing request has failed; value is afailure status indication)

In the preferred embodiment, “Cancelled”, “Failed”, and “Completed” aremutually exclusive. The system may allow a user (e.g., a systemadministrator) to only set attributes for “ToRelease” and“CancelRequested”. The other attributes may be set during requestprocessing (including cancellation processing). Downgrade requests areallowed, subject to constraints described below in Section II.D.

In step 420, the SMS/boot server 116 determines whether the new releaseor upgrade is compatible with the software presently running on thesystem. SMS/boot server 116 may perform this step by comparingcompatibility information contained in the new software release to theidentity of the software release(s) that is currently running on thesystem. FIG. 5 illustrates how this comparison may be performed in oneembodiment of the invention. Information relating to the softwarerelease(s) currently running on the system may be contained in a currentreleases portion 216 of the CDB 114, as shown in FIG. 5. Furthermore,each new software release may include an “UpgradeReleases” file 212,which identifies each release with which the new software is upwardcompatible, and a “DowngradeReleases” file 214, which identifies eachrelease with which the new software is downward compatible. Each line inthe “UpgradeReleases” file 212 may contain the unique identifier of acompatible release (e.g., in hexadecimal). The SMS/boot server 116 maycompare the current release(s) to the compatible releases contained inthe “UpgradeReleases” file. The SMS/boot server 116 will not accept arequest to upgrade from one software release to another if the currentrelease(s) running on each node in the system (and identified in the CDB114) is not identified as a compatible release.

If each node of the system is not running a compatible release, theSMS/boot server 116 will check the CDB 114 to determine whether arequest to upgrade to a compatible release is in progress, as shown instep 430. If such a request is not in progress, the upgrade procedurewill terminate, as shown in step 440. If, however, the SMS/boot server116 detects that an upgrade request to a compatible release is inprogress, an upgrade request to the new release may be queued forexecution after the current upgrade is completed, as shown in step 450.After the request in progress is completed, as shown in step 460, theSMS/boot server will initiate the rolling upgrade procedure, as shown instep 470.

In this manner, the system will not execute a rolling upgrade if anyelement of the system is not running software which is either upwardcompatible with or identical to the desired release. If and/or when thenew release is and/or becomes compatible with the current release, therolling upgrade procedure is initiated, as shown in step 470.

In one embodiment, a user may also request the cancellation of anupgrade by use of a system administration command (e.g.,“cancel_software_change”), identifying the sequence number of therequest as an argument. In one embodiment, cancellation will only takeeffect if processing of the request has not yet started, i.e., only ifthe rolling upgrade has not been initiated in step 470. A systemadministration command, “remove_software”, with the identifier of therelease as an argument, may be used to remove installed software. Thecommand will refuse to remove a release which is marked as the currentlyselected software, or which any boot machine is currently executing.

C. Performing Rolling Software Upgrades

FIG. 6 illustrates an exemplary method 600, which may be implemented bySMS/boot server 116 to upgrade software on a distributed computingsystem, according to one embodiment of the present invention. As shownin method 600, SMS/boot server 116 upgrades the software on the systemin a rolling or sequential manner, i.e., node by node. In step 610, theSMS/boot server 116 begins the upgrade process with a first node, whichmay represent any one of nodes 130 a-130 n of system 100 illustrated inFIG. 1. The SMS/boot server 116 determines whether the selected node isrunning the active release of the software (i.e., the new or upgraderelease), as shown in step 620. This information may be obtained bycommunication with the node itself or by searching the appropriate areaof the CDB 114 (e.g., the “hosts” section of the CDB 114, whichmaintains the attributes and status of the various nodes of system 100).If the selected node is not running the active release, the SMS/bootserver 116 proceeds to step 630 and determines whether the selected nodehas been “protected”.

The “protected” status may be assigned and stored as an attribute of thenodes under the “hosts” section of the CDB 114. Protected status may beassigned to a node to temporarily protect the node from rebooting if thenode contains the only active copy of a fault-tolerant service or data.In this context, the terms fault-tolerant “service” and fault-tolerant“data” may be used interchangeably. For example, a service, such as bitfile storage service (BSS), will comprise data, such as a plurality ofdata files. If a copy of any of the service or its data is determined tobe the only copy left, then the service/data will be considered to havelost its fault-tolerant status.

The “protected” status may be activated and maintained by use of the LSSand the SMS/boot server 116 (and/or by other management entities, suchas agents of the SMS). In the preferred embodiment, protected status isassigned to protect any service or data that has lost its duplicate orbackup copy within the system (i.e., lost its fault-tolerant status).Particularly, the LSS monitors the status of the various nodes,resources and services of the system 100. If any node, resource orservice fails or becomes unavailable, the LSS notifies the SMS/bootserver 116 (e.g., by updating a relational table). The SMS/boot server116 then determines which service(s) and/or data are no longeravailable. For example, if a particular node has failed, the SMS/bootserver 116 determines which services and/or data were provided by orstored on the failed node. (This information may be stored within one ormore relational tables or matrixes within the CDB 114). The SMS/bootserver 116 then locates the corresponding node(s) that provides and/orstores the surviving copy or instance of the disabled service(s) and/ordata (e.g., by use of the one or more relational tables or matrixeswithin the CDB 114), and assigns a protected status to all nodes whichprovide or store the surviving copy of the service or data. For exampleand without limitation, if a bit file storage service (BSS) disk fails,the LSS system will notify the SMS/boot server 116, which will protectthe disk(s) containing the surviving copy of the stored data, therebypreventing the reboot of any node containing any of the data until faulttolerance is restored. In this manner, no service or data provided bythe distributed computing system will be unavailable during the rollingupgrade process (i.e., at least one copy of all services and data willalways remain available).

Referring back to FIG. 6, if the node is not protected in step 630, theSMS/boot server 116 loads the new or target software release onto thenode and reboots the node, thereby upgrading the node to the targetsoftware, as shown in step 640. If the node is protected, the SMS/bootserver 116 does not attempt to upgrade the node, but rather sets a retryindicator, as shown in step 650. The retry indicator may be stored inthe CDB 114 and may identify the protected node. The retry indicator iseffective to notify the SMS/boot server 116 that the node was notupgraded and that the upgrade process is not complete. Once the node hasbeen rebooted (i.e., during a software upgrade), the retry indicatorwill be cleared. Following the upgrade of a node (e.g., step 640) or thesetting of a retry indicator (e.g., step 650), SMS/boot server 116proceeds to the “next” node in the system, as shown in step 660. TheSMS/boot server 116 will then repeat steps 620-660.

The “next” node referred to in step 660 may be selected in any manner,based on any suitable or desired priority system. In one embodiment, anadministrator may specify an ordering of upgrades of components throughan administrative interface (e.g., interface 230). For example, anadministrator might select to upgrade all of one class of component,such as a BSS, before upgrading other classes of components.

If, in step 620, the SMS/boot server 116 detects that the selected nodeis running the active software release, it proceeds to step 670. TheSMS/boot server 116 then determines whether all retry indicators are“off” or cleared and whether all nodes in the system are running theactive release. The SMS/boot server 116 may perform this step bychecking the CDB 114. If the SMS/boot server 116 detects that one ormore retry indicators are set or that any nodes are not running theactive release, it proceeds to the next node (step 660), and repeatssteps 620-670. Once all the retry indicators are “off” and all nodes arerunning the active release, the upgrade procedure will terminate, asshown in step 680.

The presence of failed servers does not affect the upgrade process, aslong as the SMS/boot server 116 and CDB 114 are properly updated.Particularly, the SMS/boot server 116 will effectively “skip over” orignore any failed servers during the upgrade process. However, it shouldbe appreciated that if a failed server contains one of two instances ofa service or data, the failure of that node will cause any other nodeproviding the surviving copy of the service or data to be “protected”.If the failed server is down for an extended period of time (e.g., morethan some predetermined period of time), the SMS/boot server 116 mayreplace it with a spare machine or node, by copying all of theinformation from the active node(s) to the new node(s), and thenrebooting the new node(s) with the upgraded software.

D. Downgrade Requests

Downgrade requests may be entered via the system administration command“downgrade_software”, with a release identifier as its argument. Thedowngrade process is substantially similar to the afore-describedupgrade process. Specifically, the SMS/boot sever 116 will only initiatethe downgrade request if the request is for a release which iscompatible with the presently operating software. This may be determinedby comparing the target release to information contained in thepresently running release. Particularly, each software release mayinclude a “DowngradeReleases” file in the top of its subtree (e.g., inthe same format as the “UpgradeReleases” file), providing the set ofrelease identifiers to which it may be downgraded. If the downgraderequest is for a release that is found in the “DowngradeReleases” file,the SMS/boot server 116 will initiate the downgrade request.

The SMS/boot server 116 will perform the downgrade in a sequential orrolling manner (e.g., in a manner substantially similar to method 600).That is, the SMS/boot server 116 will downgrade each node in the system,one at a time, and will “skip over” any “protected” nodes. The SMS/bootserver 116 will set a retry indicator for the protected nodes, and willcontinue the process until all nodes have been downgraded. In oneembodiment, a given node is downgraded by shutting down all services onthe node other than the LSS and the SMS Agent, and then executing a“downgrade-release” script with the target release identifier as anargument. The “downgrade-release” script is effective to downgrade thesoftware to the target release. Once the “downgrade-release” script hascompleted, it signals completion by making an update in a table (e.g., a“ReleaseLevel” table) within the LSS, giving the destination releaselevel, and then “shuts down” the node. When the SMS/boot server 116notices that the node has shutdown, it records the node as being at thetarget release level (e.g., within the CDB 114), conveys thatinformation to the boot servers, and reboots the machine. In the case ofa boot machine, the downgrade script adjusts the boot machine's ownconfiguration to use the new release on next boot before shutting downthe system.

In this manner, the present invention provides a system and method formanaging software upgrades in a distributed computing system thatperforms software upgrades on a node by node basis, in a manner whichallows all services and data provided by the distributed computingsystem to remain available throughout the upgrade process. The systemand method will automatically protect any node that provides the onlyinstance of a service or data during the upgrade process, therebypreventing the node from being rebooted until fault tolerance isrestored. In this manner, all services and information will remainavailable during the upgrade process. In a similar manner, the presentinvention is further able to perform software downgrades throughout thesystem in a manner which allows the system and all of its components toremain available throughout the downgrade process.

Although the present invention has been particularly described withreference to the preferred embodiments thereof, it should be readilyapparent to those of ordinary skill in the art that changes andmodifications in the form and details may be made without departing fromthe spirit and scope of the invention. For example, it should beunderstood that Applicant's invention is not limited to the exemplarymethods that are illustrated in FIGS. 3, 4 and 6. Additional ordifferent steps and procedures may be included in the methods, and thesteps of the methods may be performed in any order suitable to achieverolling upgrades while allowing the distributed computing and itscomponents to remain available. It is intended that the appended claimsinclude such changes and modifications. It should be further apparent tothose skilled in the art that the various embodiments are notnecessarily exclusive, but that features of some embodiments may becombined with features of other embodiments while remaining with thespirit and scope of the invention.

1. A system for managing a software upgrade in a distributed computingsystem having a plurality of nodes that provides a plurality offault-tolerant services, wherein a first set of nodes providing a firstfault-tolerant service can differ from, yet can also overlap with, asecond set of nodes providing a second service, and wherein making anupgrade current on a given node can take an amount of time sufficient tobe considered a fault if not otherwise masked by fault-tolerance, thesystem comprising: at least one node which is communicatively connectedto the plurality of nodes and which is configured to receive a softwarerelease, and to upgrade each of the plurality of nodes with the softwarerelease in a sequential manner, accounting for the possibility ofdifferent versions of software running on different nodes of the system,whereby the plurality of fault-tolerant services remain available whilethe software upgrade is in progress a service which is configured tonotify the at least one node when a first copy of fault-tolerant servicebecomes unavailable; and wherein the at least one node is configured toassign a protected status to a node including any portion of a survivingcopy of the fault-tolerant service, the protected status being effectiveto prevent the node from being upgraded.
 2. The system of claim 1wherein service is further configured to notify the at least one nodewhen the first copy of the fault-tolerant service is restored, andwherein the at least one node is configured to remove the protectedstatus of the affected nodes once fault-tolerant status is restored. 3.The system of claim 1 wherein the at least one node is furtherconfigured to determine whether the software release is compatible withthe current software running on the plurality of nodes and to upgradethe plurality of nodes only if the software release is compatible withthe current software.
 4. The system of claim 3 further comprising: aconfiguration database which is communicatively coupled to the at leastone node and which stores information regarding the plurality of nodes.5. The system of claim 4 wherein the at least one node comparescompatibility information contained in the software release toinformation identifying the current software running on the plurality ofnodes, which is stored in the configuration database, to determinewhether the software release is compatible with the current softwarerunning on the plurality of nodes.
 6. The system of claim 3 wherein theat least one node is further configured to detect when a first upgradeto a compatible software is in progress, and to upgrade the plurality ofnodes to the software release once the first upgrade is complete.
 7. Thesystem of claim 1 wherein the at least one node is configured to upgradea node by loading the software upgrade onto the node and rebooting thenode.
 8. The system of claim 1 wherein the at least one node whichupgrades the nodes in the system includes a first node and at least onesecond node, wherein the first node has primary responsibility forperforming upgrades and wherein the at least one second node acts as abackup.
 9. The system of claim 1 further comprising a plurality ofagents which are respectively disposed on the plurality of nodes andwhich are configured to assist in upgrading the nodes with the softwareupgrade under remote control of the at least one node.
 10. The system ofclaim 1 further comprising an interface which is communicativelyconnected to the at least one node, and which is configured to allow auser to enter an upgrade request, effective to cause the at least onenode to initiate an upgrade to the software release.
 11. The system ofclaim 10 wherein the interface is further configured to allow a user toenter a downgrade request, effective to cause the at least one node todowngrade the software currently running on the plurality of nodes in asequential manner, whereby none of the fault-tolerant services becomesunavailable while the downgrade is in progress.
 12. A method formanaging a software upgrade in a distributed computing system having aplurality of nodes that provide a plurality of fault-tolerant services,wherein a first set of nodes providing a first fault-tolerant servicecan differ from, yet can also overlap with, a second set of nodesproviding a second service, and wherein making an upgrade current on agiven node can take an amount of time sufficient to be considered afault if not otherwise masked by fault-tolerance, the method comprisingthe steps of: receiving a new software release; upgrading each of theplurality of nodes with the new software release in a sequential manner,accounting for the possibility of different versions of software runningon different nodes of the system, whereby the plurality offault-tolerant services remains available while the software upgrade isin progress determining whether a first copy of a fault-tolerant servicehas become unavailable; and preventing any node having a surviving copyof the fault-tolerant service from being upgraded while the first copyof the fault-tolerant service is unavailable.
 13. The method of claim 12further comprising the steps of: detecting that a previously unavailablecopy of a fault-tolerant service has recovered; and upgrading any nodehaving the surviving copy of the fault-tolerant service.
 14. The methodof claim 12 further comprising the step of: determining whether the newsoftware release is compatible with a current software release that isbeing run on the distributed computing system; and performing thesoftware upgrade only if the new software release is compatible with thecurrent software release that is being run on the distributed computingsystem.
 15. The method of claim 14 further comprising the step of:determining whether a first software upgrade to a compatible newsoftware release is in progress; waiting for the first software upgradeto be completed; and performing a second software upgrade to anothersoftware release.
 16. The method of claim 12 wherein the step ofupgrading a node includes loading the new software release onto the nodeand rebooting the node.
 17. The method of claim 12 wherein the newsoftware release comprises a patch release.
 18. A method for managing asoftware upgrade in a distributed file system having a plurality ofnodes, which provide a plurality of fault-tolerant services, wherein afirst set of nodes providing a first fault-tolerant service can differfrom, yet can also overlap with, a second set of nodes providing asecond service, and wherein making an upgrade current on a given nodecan take an amount of time sufficient to be considered a fault if nototherwise masked by fault-tolerance, comprising: receiving a newsoftware release; determining whether the new software release iscompatible with a current release running on the distributed filesystem; initiating a rolling upgrade process if the new software releaseis compatible; performing the rolling upgrade process by sequentiallyloading and rebooting each of the plurality of nodes with the newsoftware release; accounting for the possibility of different versionsof software running on different nodes of the system; and ensuring thatthe plurality of fault-tolerant services remains available throughoutthe rolling upgeade process services remains available throughout therolling upgrade process includes the steps of: determining whether afirst copy of a fault-tolerant service has become unavailable; andpreventing any node having a surviving copy of the fault-tolerantservice from being upgraded while the first copy of the fault-tolerantservice is unavailable.
 19. The method of claim 18 wherein the pluralityof fault-tolerant services includes services selected from the groupconsisting of bit file storage services, metadata services and gatewayservices.